Auto-resonant peniotron having amplifying waveguide section

ABSTRACT

In a peniotron, a hollow electron beam is generated from a cathode gun assembly and a DC magnetic field is applied to the electron beam from solenoid coils. Thus, each electron of the electron beam is gyrated into a resonant cavity and into propagating waveguide sections which are maintained in auto-resonant conditions so that the electrons interact with an electromagnetic waves of TE mode not only in the resonant cavity section but also in a waveguide section. Accordingly, the electromagnetic wave is oscillated in the resonant waveguide section and amplified in the propagating waveguide section in such a manner that the level of the electromagnetic wave in the resonant cavity section is far less than the output power from said propagating waveguide.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an extremely high frequency oscillatorand, more particularly to an extremely high frequency oscillator havinga high frequency circuit assembly comprising a resonant cavity and awaveguide, wherein each electron gyrating within a DC magnetic fieldinteracts with TE-mode electromagnetic waves propagating within the highfrequency circuit assembly, thereby to oscillate electromagnetic waveshaving wavelengths in the order of millimeters to submillimeters.

2. Description of the Related Art

One of the known electron tubes of this type is a peniotron. As isdisclosed in Japanese Patent Publication No. 45-35334 and JapanesePatent Disclosure No. 61-273833, a peniotron is a high power electrontube which comprises a high frequency circuit assembly and oscillates oramplifies electromagnetic waves by virtue of the phase-separation effectresulting from the interaction between electrons gyrating within a DCmagnetic field and the electromagnetic waves propagating within thecircuit assembly.

The peniotron utilizes the effect resulting from the movements ofguiding centers around which electrons gyrate in a spatiallynon-uniform, high frequency electromagnetic field. Each electron isalternately accelerated and decelerated every time it gyrates around theguiding center. The accelerations and decelerations of each electron aregradually accumulated. In this interaction, the successive decelerationis stronger than the previous acceleration. A kinetic energy of eachelectron corresponding to accumulated deceleration is converted into thehigh frequency electromagnetic energy. The essential feature of theoperating mechanism of the peniotron is the energy exchange between theindividual electrons and the high frequency electromagnetic field. Theoperating mechanism of the peniotron is basically different from that ofthe klystron or the gyrotron in which the electromagnetic field isamplified or oscillated because a bunching of electrons interacts withthe electromagnetic field. Hence, the peniotron can perform an operationwherein electrons act, independent of a phase relationship between theelectrons and the high frequency electromagnetic field. All of theelectrons are therefore trapped within the deceleration electric fieldof the electromagnetic waves due to the phase-separation effect. Intheory, all gyrating kinetic energy of the electrons can be convertedinto the energy of the electromagnetic waves. In view of this, theefficiency of the energy conversion, from the electrons to theelectromagnetic waves, can be expected to be extremely high.

The conventional oscillator, described above cannot convert the kineticenergy acting in the longitudinal direction of the tube into the energyof electromagnetic waves. It is impossible with the prior-art oscillatorto increase the energy-conversion efficiency to a near-100% value,unless the oscillator is equipped with a perfect depressed collector.Another problem with the conventional oscillator is that the higher thefrequency of the electromagnetic waves, the smaller the resonant cavityand waveguide of the high frequency circuit assembly should be. Thesmaller the resonant cavity and the waveguide, the lower the electricpower capacity, because a permissible electric power loss of the circuitis restricted. Further, the oscillator requires an intense DC magneticfield, and the frequency of the electromagnetic waves is limited. Theoscillators, developed thus far, can output 10 kW at an operatingfrequency of 45 GHz at best.

SUMMARY OF THE INVENTION

Accordingly, it is the object of this invention to provide a high-power,extremely high frequency oscillator which satisfies auto-resonantconditions required for oscillating high frequency electromagnetic wave.Another object of the present invention is to provide such an oscillatorwhich has an energy-conversion efficiency as high as a theoreticalenergy-conversion efficiency of the peniotron, and which can oscillateelectromagnetic waves having wavelengths in the order of millimeters tosub-millimeters.

According to the present invention, there is provided an extremely highfrequency oscillator, in which each of gyrating electrons, i.e.,circulating and traveling electrons, and TE-mode electromagnetic wavesinteract within a high frequency circuit assembly, satisfyingauto-resonant conditions when the phase velocity Vp of the waves isequal to, or nearly equal to, the light velocity c. The high frequencycircuit assembly comprises a resonant cavity and a propagating waveguideconnected to the downstream-end of the cavity. The high frequency powerbeing oscillated in the cavity is sufficiently suppressed to a valueless than that of the high frequency power being output from thewaveguide. The extremely high frequency oscillator of this invention isnamed as an auto-resonant peniotron in this specification.

The oscillator performs a preliminary, low-power oscillation within theauto-resonant cavity. More specifically, electrons interact in thecavity to a relatively low degree, with a TE-mode electromagnetic fieldpropagating along the beam. Accordingly, reflection electromagneticwaves produced in the cavity do not affect the auto-resonant conditionsso that the auto-resonant conditions are always maintained The behaviorvariations of the electrons are suppressed. The oscillating power levelin the cavity can be set by selecting Q value of the cavity A beam ofthe electrons passing through the cavity and the electromagnetic wavesare merged in the propagating waveguide. In the waveguide, the beam andthe wave interact while maintaining the auto-resonant conditions.Therefore, not only the circulating kinetic energy of the electrons, butalso the traveling kinetic energy of the electrons serve to intensifythe electromagnetic field within the propagating waveguide. Hence, theoscillator has a high energy-conversion efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a peniotron according to thepresent invention;

FIG. 2 is a graph explaining how the kinetic energy of electrons changesas the electrons travel within the propagating waveguide shown in FIG.1, in the axial direction of the oscillator;

FIG. 3 is a graph representing the relationship between the oscillatingpower in the resonant cavity of the peniotron and the energy-conversionefficiency of the peniotron; and

FIGS. 4, 5, and 6 are also graphs showing the operating characteristicof another peniotron according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the invention will now be described in detail, withreference to the accompanying drawings.

FIG. 1 schematically illustrates a peniotron, which is an embodiment ofthe present invention As is shown in FIG. 1, the peniotron comprises anelectron gun assembly 11, a beam-guiding section 12 coupled to the gunassembly 11, and a resonant cavity section 13 connected to thebeam-guiding section 12. The electron gun assembly 11 extends in theaxis z of the peniotron. The beam-guiding section 12 guides the electronbeam emitted from the assembly 11 into the resonant cavity section 13.

The peniotron further comprises a propagating wave guide 14 connected tothe downstream end of the section 13, a collector section 15 coupled tothe output end of the waveguide 14, and an output waveguide 17 coupledto the output end of the collector 15. The propagating waveguide 14 hasthe same cross section as the resonant cavity section 13 and thecollector section 15 is designed to collect electrons. A window 16,which is a dielectric member, is located within the junction between thecollector section 15 and the output waveguide 17, and attached inairtight fashion to the inner surface of the junction

The peniotron further comprises three solenoid coil units 18, 19, and20. The coil units 18 and 19 surround the electron gun assembly 11. Thecoil unit 20 surrounds both the resonance cavity section 13 and thepropagating waveguide 14.

The electron gun assembly 11 has a cathode 21 and an accelerating anode22. The cathode 21 emits electrons from its circumferential region whenit is heated The anode 22 accelerates the electrons emitted from thecathode 21. As a result, the electron gun assembly 11 emits a hollowelectron beam e. The solenoid coil units 18 and 19, both surrounding theelectron gun assembly 11, generate DC magnetic fields havingpredetermined intensities. Due to these DC magnetic fields, eachelectron of the hollow electron beam e is gyrated. The solenoid coilunit 20 generates a DC magnetic field having a predetermined intensityand extending almost parallel to the axis z of the peniotron, whichcauses the electrons of the electron beam e to gyrate at predeterminedcycles. The resonant cavity section 13 and the propagating waveguide 14have inner diameters far greater than the wave length of theelectromagnetic waves oscillated in the peniotron. This enables theelectromagnetic waves of a predetermined mode to propagate through thewaveguide 14 at a phase velocity Vp which is nearly equal to lightvelocity c. As a result, the interior of the cavity and waveguideremains under auto-resonant conditions. The electromagnetic wavesoscillated in the peniotron shown in FIG. 1 have a predetermined mode inwhich a high frequency electric field is more intense in a region remotefrom the gyrating center around which an electron circulates, than in aregion close to that center. Examples of such modes are: the TEll modefor a waveguide having a rectangular cross section, and TE21 mode for awaveguide having a circular cross section.

The interaction occurs in the resonant cavity section 13 between thegyrating electron and the electromagnetic waves of a specified mode.This electron-wave interaction imparts part of the kinetic energy of theelectron to the electromagnetic wave. Electromagnetic waves of specificstrength and mode are thereby oscillated. The electromagnetic waves thusoscillated propagate and the electron beam travels from the resonancecavity 13 into the waveguide 14. In the waveguide 14, the waves interactwith the electron beam and are intensified or amplified.

The peniotron, which operates as has been described, can convert thekinetic energy of the electrons to the energy of electromagnetic waveswith a high efficiency. It will be explained how the peniotron achievesa high energy-conversion efficiency.

As has been pointed out, the kinetic energy of the electron beam isconverted into that of electromagnetic waves in two steps. First, partof the kinetic energy is imparted to the electromagnetic waves withinthe resonant cavity section 13. Then, the rest of the energy is impartedto the electromagnetic waves within the propagating waveguide 14connected to the downstream end of the resonant cavity section 13. FIG.2 shows the relationship between the kinetic energy Eel of the electronbeam and the position within the waveguide 14, the relationship havingbeen determined by computer simulation wherein the mode TE21 wasselected for the waveguide 14 and auto-resonant conditions were set.FIG. 2 illustrates how the average kinetic energy of 24 sample electronshaving different incidence phases in respect to the TE mode changes asthey travel through the waveguide 14 along the axis z thereof, towardthe output end of the waveguide 14. As the curve shown in FIG. 2indicates, all gyrating electrons forming the beam impart theirrespective energies to the electromagnetic waves and then loseenergy--substantially at the same time, as if a single electron gavegreat energy to the electromagnetic waves and lost its energy. As isevident from FIG. 2, the peniotron achieved a maximum energy-conversionefficiency of 95%. As the results of the computer simulation suggest,the peniotron shown in FIG. 1 can convert the kinetic energy of anelectron beam to that of electromagnetic waves with an efficiency whichis nearly equal to 100%, if the peniotron is maintained under an optimumoperation condition.

This high energy-conversion efficiency could not be attained if allkinetic energy of the electron beam were converted into high frequencyenergy corresponding to the whole output power of the peniotron, in thecavity section 13 only. The inventors hereof conducted a computersimulation to determine the efficiency at which all kinetic energy ofthe beam could be converted to high frequency energy in the resonancecavity section 13 only. The results of this simulation was a conversionefficiency of 67% at most. This is because no auto-resonant conditionscan be set within the cavity section 13. More precisely, this isbecause, as the electrons interact with the electromagnetic waves inonly the resonant cavity section 13, their kinetic energies arenon-uniformly decreased by the reflection waves generated in the cavitysection 13 so that the kinetic energies of the electrons cannot beuniformly converted into the electromagnetic wave. Thus, it is confirmedby the inventors that the non-uniformity of the kinetic energies isproduced after almost all of the kinetic energy has been converted intothe electromagnetic energy and the electrons have decreased kineticenergies.

In the oscillator shown in FIG. 1, the electromagnetic wave isoscillated in the cavity at low power and the remaining kinetic energiesare almost all converted into the electromagnetic wave in the waveguidesection 14. Accordingly, it is possible that the oscillator has a highenergy-conversion efficiency, as shown in FIG. 2.

FIG. 3 is a graph representing the relationship between theenergy-conversion efficiency η and the power oscillated in the resonancecavity section 13, the relationship being the result of the computersimulation. In this simulation, the target high frequency power was setat about 6.4 MW. As can be understood from FIG. 3, the energy-conversionefficiency can be maintained over 90% when 8% or less, or preferably 4%or less (needless to say, not 0%), of the target output power isoscillated within the resonance cavity section 13.

Apart from the high energy-conversion efficiency, the peniotron shown inFIG. 1 has other advantages. First, it can have a greater tube-diameterthan the prior-art peniotron, since the electron interacts with theelectromagnetic waves under the auto-resonant conditions in the highfrequency circuit assembly, the assembly comprising the resonance cavitysection 13 and the propagating waveguide 14. Secondly, it needs only aDC magnetic field which is far less intense than is required in theprior-art peniotron to oscillate electromagnetic waves at the samefrequency, from a highpower electron beam. Therefore, the peniotron canoscillate electromagnetic waves, even at wavelengths in thesub-millimeter order, with high efficiency.

The present invention is not limited to the embodiment illustrated inFIG. 1. For instance, the solenoid coil unit 20 can be replaced by aplurality of solenoid units which are arranged along the axis z of thepeniotron. In this case, the coil units generate magnetic fields whoseintensities differ such that these magnetic fields form a DC magneticfield extending along the axis z and having a tapered intensitydistribution Bz at the downstream side of the waveguide 14 as shown inFIGS. 4, 5 and 6. In the actual waveguide, it is confirmed that thephase velocity Vp of the electromagnetic wave is greater than the lightvelocity c. Thus, in the conventional peniotron, the ideal autoresonantconditions cannot be obtained. However, the auto-resonant condition canbe obtained if the DC magnetic field has the tapered intensitydistribution according to the embodiment of the invention. Accordingly,this embodiment can also attain a sufficiently high energy-conversionefficiency, as will be understood from FIGS. 4, 5 and 6 which representthe results of the simulation conducted by the inventors.

In the simulation, the phase velocity Vp was set at 1.05 times the lightvelocity c, the TE21 mode was selected, and the oscillation frequencyand the acceleration voltage were set at 200 GHz and 1 MV, respectively.Further, the ratio of the velocity at which the electrons arecirculated, to the velocity at which they move along the axis z wasselected to be 1.109, and the intensity of the magnetic field in theupstream end of the waveguide and the inner diameter of the waveguidewere set at 8.41 Tesla and 2.39 mm, respectively.

FIG. 4 illustrates how the high frequency power P and the DC magneticfield Bz are distributed in the waveguide 14 when the high frequencypower supplied to the waveguide 14 from the cavity 13 is 1 kW.Similarly, FIG. 5 shows how the power P and the magnetic field B aredistributed in the waveguide 14 when the high frequency power suppliedto the waveguide 14 from the cavity 13 is 10 kW. FIG. 6 represents howthe power P and the magnetic field are distributed in the waveguide 14when the high frequency power supplied to the waveguide 14 from thecavity 13 is 100 kW. More specifically, in each of these FIGURES,intensity curves 1, 2, and 3 indicate the intensity distribution of theDC magnetic field Bz which are set when the electron-beam current is 1A, 10 A, and is 100 A, respectively. Further, in each of FIGS. 4, 5, and6, power curves 1, 2, and 3 represent the distributions of the highfrequency power P which are calculated from the intensity distributionswhen the electron-beam current is 1 A, 10 A, and is 100 A, respectively.

As can be seen from FIGS. 4, 5, and 6, the high frequency power Pincreases as the electron beam travels toward downstream-end of thewaveguide. This is because the DC magnetic field is maintained atsubstantially constant level in the upstream portion of the waveguide 14and gradually decreased in the downstream portion of the waveguide 14.The magnetic field is held almost at substantially constant level in theupstream portion of the waveguide in which the electron beam interactswithin the electromagnetic waves to a low degree. By contrast, themagnetic field is decreased gradually in the downstream portion in whichthe interaction between the beam and the electromagnetic waves isincreased and the auto-resonant conditions which are changed due to thechanges of the electron mass and the velocity of the electrons, arecorrected by the tapered distribution 1, 2 or 3 of the curve Bz. Hence,the peniotron according to the second embodiment can also attain a highenergy-conversion efficiency and output a high frequency power.

As has been explained, the peniotron according to invention comprises ahigh frequency circuit assembly having a resonant cavity section and apropagating waveguide connected to the downstream end of the resonancecavity section. In the circuit assembly, electrons gyrate, andelectromagnetic waves are oscillated and amplified The electrons and thewaves interact, while satisfying conditions required for auto-resonance.More specifically, the electron beam interacts with the electromagneticwaves to a low degree in the cavity and the upstream portion of thewaveguide, generating a high frequency power of a value far less thanthe target value, and then interacts with the waves to a sufficientdegree in the downstream portion of the waveguide, thereby generating ahigh frequency power of the target value. It is possible that both theresonant cavity section and the propagating waveguide have innerdiameters greater than those of their counterpart incorporated in theconventional peniotron. Due to the two-step interaction between theelectron beam and the electromagnetic waves, and also the use of theresonant cavity section and the waveguide, both having a large innerdiameter, the peniotron according to the invention can convert anelectron beam into high frequency high power with high energy-conversionefficiency.

What is claimed is:
 1. An extremely high frequency oscillatorcomprising:beam-generating means for generating a beam of electrons anddirecting the electrons in a predetermined direction; means for applyinga DC magnetic field to the electrons generated by said beam-generatingmeans, thereby causing each of the electrons to gyrate along thepredetermined direction; energy-converting means for causing theelectrons to interact with an electromagnetic wave of TE mode, therebyto convert kinetic energy of the gyrating electrons into energy of theelectromagnetic wave, said energy-converting means including a resonantcavity section and a propagating waveguide section connected to theresonant cavity section, auto-resonant conditions being preserved in theresonant cavity and propagating waveguide sections, theelectromagnetic-wave being oscillated in said resonant cavity sectionand amplified in the propagating waveguide section, the electromagneticwave in the resonant cavity section having a power level which is lessthan an output power of the electromagnetic wave from said propagatingwaveguide section; and electro-collecting means for collecting theelectrons from the propagating waveguide section.
 2. The extremely highfrequency oscillator according to claim 1, wherein the power level ofthe electromagnetic-wave oscillated in said resonant cavity section is8% or less (but not 0%) of the electromagnetic-wave output power fromsaid propagating waveguide section.
 3. The extremely high frequencyoscillator according to claim 1, wherein the DC magnetic field extendsthrough said propagating waveguide section and becomes less intensegradually toward the output end thereof at the downstream side of theelectron beam.
 4. The extremely high frequency oscillator according toclaim 1, wherein said beam-generating means generates a hollow electronbeam.